Detail View: NASA Astronomy Picture of the Day Collection: M101: The Pinwheel Galaxy

Title: 
M101: The Pinwheel Galaxy
Explanation: 
Why do many galaxies appear as spirals [ http://antwrp.gsfc.nasa.gov/apod/lib/spirals.html ]? A striking example is M101, shown above [ http://www.astr.ua.edu/gifimages/m101b.html ], whose relatively close distance of about 22 million light years allow it to be studied in some detail. Recent evidence [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997ApJ%2E%2E%2E481%2E%2E169W&db_key=AST&nosetcookie=1 ] indicates that a close gravitational interaction with a neighboring galaxy created waves of high mass [ http://lsnt7.lightspeed.net/~astronomy/galaxy.notes/galaxy.notes.html#A1.1.5.1 ] and condensed gas which continue to circle the galaxy [ ftp://crux.astr.ua.edu/web/goodies/data_resources/galaxies.text ]. These waves compress existing gas and cause star formation [ http://antwrp.gsfc.nasa.gov/apod/ap970119.html ]. One result is that M101 [ http://antwrp.gsfc.nasa.gov/apod/ap970608.html ], also called the Pinwheel Galaxy, has several extremely bright star-forming regions (called HII regions) spread across its spiral arms. M101 [ http://www.seds.org/messier/m/m101.html ] is so large that its immense gravity distorts smaller nearby galaxies.
Credit and Copyright: 
W. Keel (U. Alabama in Tuscaloosa), KPNO [ http://www.noao.edu/kpno/kpno.html ], 4-m Mayall Telescope [ http://www.noao.edu/kpno/pubpamph/pub.html ]
facet_where: 
Alabama
facet_what: 
Crux
original url: 
http://antwrp.gsfc.nasa.gov/apod/ap970805.html
UID: 
SPD-APOD-ap970805